How were you watching Letterman every night in high school? Wasn't it on a little late? I think by high school I was watching Johnny's monologue and then going to bed. I watched the whole show and Letterman on Friday nights only. You must have been operating on no sleep!
I used to be the only member of my family who could understand the eternal mystery of setting the VCR to record a program in advance. I did record Letterman quite a bit, either for myself or my brother. He was funnier when you watched him late at night than after school, thought.